1. Field of the Invention
The present invention relates generally to an optical pick-up device, and more particularly, to an improved optical pick-up device for reading and/or writing information to and from a recording medium, in which a lens holder that holds a lens that focuses light onto a recording surface of the recording medium is movably supported by cantilever springs.
2. Description of the Related Art
In for example CD-ROM or CD-RW disk drive units in which a rotating disk-like recording medium (hereinafter simply disk) is loaded, a laser beam is projected onto the disk and information is recorded (written) onto the disk or reproduced (read) from the disk. The optical pick-up device installed in such types of disk drive units includes, among other components, an object lens that directs a laser beam emitted from a laser diode onto the disk. The orientation of the object lens is adjusted so that the focus of the light directed onto the disk by the object lens coincides with a recording surface of the disk.
In other words, an optical pick-up device performs focus control and tracking control so that the object lens follows changes in the track due to eccentricities in the rotation of the disk and/or wobble due to rotation of the disk. This type of control of the object lens is performed by an actuator using an electromagnetic force, the actuator being typically composed of a combination of a coil and a magnet.
A lens holder that supports the object lens is made compact and lightweight in order to facilitate focus and tracking control, with four wire-like elastic supports (that is, cantilever springs) arranged in parallel forming a supporting structure that supports the lens holder and that moves minutely in either a focus direction or a tracking direction, as the case may be, by the driving force from the actuator.
Further, the lens holder is placed so as to be contained within a frame formed into the shape of the letter U, the open portion being at a proximal end. Base portions of the four wire-like elastic supports are joined to a suspension fixedly mounted on a distal end of the frame, with tip portions joined to the lateral surfaces of the lens holder. As a result, the lens holder is supported by the four wire-like elastic supports in such a way as to be movable in a direction parallel to the frame.
However, a drawback of the above-described conventional optical pick-up device is that, when installed in a laptop personal computer or other similar portable apparatus and such apparatus is dropped during handling, the movement of the lens holder caused by such an impact on the pick-up unit is greater than that which is normally imparted thereto, thus damaging the wire-like elastic supports.
It is possible to provide the lens holder with lateral projections protruding therefrom, so that the projections contact the frame so as to restrict the range of movement of the lens holder and thus prevent the lens holder from being damaged by excessive movement. However, if the center of gravity of the lens holder and the center drive point of the actuator diverge from each other, an angular moment comes into play around the projection after the projection contacts the frame, thus twisting or rotating the lens holder around the tip of the projection and thereby deforming the wire-like elastic supports.
With the disk drives installed in laptop personal computers in particular, in which a seek direction (that is, the tracking direction) of the optical pick-up is slanted at approximately a 45 degree angle with respect to a front panel of the disk holder (thus taking advantage of the additional length afforded by using a corner of the disk drive unit frame instead of a lateral side of the frame), the direction of the shock of impact upon dropping the laptop (assuming the laptop is dropped on the front panel of the disk holder) and the direction of drive of the actuator are at approximately a 45 degree angle with respect to each other. In short, the structure easily allows an angular moment to be generated about the tip of the projection of the lens holder, thereby deforming the wire-like elastic supports.
If the wire-like elastic supports are thus deformed, then the positioning and angle of the lens can change and information can no longer be written to or read from the disk.
It is possible to use relatively thick wire for the wire-like elastic supports so as to prevent the wire-like elastic supports from being deformed by the shock of impact. However, the thicker the wire the more rigid the wire-like elastic support, which makes it more difficult to move the primary resonance frequency (at which focus control and tracking control low-frequency sensitivity tends to deteriorate) to a desired frequency.
In order to set the primary resonance frequency to a desired frequency and prevent focus control and tracking control low-frequency sensitivity from deteriorating, the longer the suspension the better. However, the conventional optical pick-up typically installed in an ordinary laptop computer, and particularly the recording pick-up, has a substantial number of mounted parts, thus limiting the space available to lengthen the suspension.
More specifically, there is limited space in which to accommodate the optical pick-up devices of the disk drive units typically installed in laptop computers. Optical pick-up devices of optical disk drive units that can record are becoming more common, but these, too, have the disadvantage of a large number of component parts as compared to the read-only type of optical pick-up device, thus placing additional constraints on the already limited amount of space available for installation. For both these reasons, the wire-like elastic supports can be neither lengthened nor thickened. Additionally, thickening the wire-like elastic supports reduces their sensitivity, which is undesirable.